The evidence for prescription of Long Term Oxygen Therapy is well
established whereas the evidence for supply of ambulatory and training
oxygen is less robust. There is increasing evidence that the use of
these latter therapies is beneficial although guidelines for supply are
limited. This paper aims to review the evidence base for ambulatory and
training oxygen and to suggest guidelines for assessment and
prescription based on our local research and experience in Aotearoa/New
Zealand. Young P (2005). Ambulatory and training oxygen: a review of the
evidence and guidelines for prescription. New Zealand Journal of
Physiotherapy 33(1) 7-12. Key Words: Ambulatory oxygen, training oxygen,
exercise, pulmonary rehabilitation.

Key Points

* There is increasing evidence that the use of training and
ambulatory oxygen improves rehabilitation outcomes.

* A standarised assessment process is outlined with the view to
optimising clinical benefit and resource use.

INTRODUCTION

The evidence for prescription of Long Term Oxygen Therapy (LTOT) is
well established (Medical Research Council Working Party 1981, Nocturnal
Oxygen Therapy Trial Group 1980) in contrast to that for ambulatory and
training oxygen. With regard to the latter forms of oxygen therapy,
patients with chronic respiratory disease who desaturate significantly
on exertion may benefit from the provision of oxygen during activity
through improved exercise tolerance and reduced dyspnoea during exercise
or activities of daily living. Supply of oxygen in this context has been
variably described. The American Thoracic Society (1995) criteria for
provision of oxygen during exercise suggest that supplemental oxygen
should be provided for patients who demonstrate arterial oxygen
saturation at or below 88% during exercise. The Royal College of
Physicians guidelines (1999) define ambulatory oxygen as oxygen therapy
during exercise and activities of daily living and recommend provision
when arterial saturations fall below 90% on exertion. It is important to
clarify the distinction between an oxygen supply which is available for
the patient at home or out of the home and that which is provided as
part of a pulmonary rehabilitation programme. For purposes of this
discussion, training oxygen is that supplied for use during the exercise
component of pulmonary rehabilitation and ambulatory oxygen is that
which is supplied for activities of daily living, which might include
exercise outside the home environs.

There is increasing evidence that the use of training and
ambulatory oxygen is beneficial although guidelines for supply are
limited. This paper aims to review the evidence base for training and
ambulatory oxygen and to suggest guidelines for assessment and
prescription based on the Auckland research group experience.

Exercise and respiratory disease

Pulmonary rehabilitation is an integral component of the medical
management of patients with chronic obstructive pulmonary disease (COPD). It has been shown to reduce disability and handicap and hence
improve quality of life. There is strong supporting evidence to
demonstrate significant improvement in exercise performance and
reduction in the perception of dyspnoea (ACCP/AACVPR 1997, Lacasse et
al., 1996). Although the majority of evidence is related to COPD it
seems reasonable that this could be extrapolated to other respiratory
diseases such as pulmonary fibrosis and bronchiectasis.

Exercise training is the cornerstone of pulmonary rehabilitation
(American Thoracic Society 1999). Muscle weakness and atrophy are common
in patients with chronic respiratory disease and significantly
contribute to impaired exercise performance (Gosselink et al., 2000).
The training effect depends on the specificity of exercise and the
intensity of exercise where only a load higher than baseline will
achieve a training effect. Although improvements in quality of life and
exercise tolerance have been achieved with low intensity exercise
programmes or symptom limited programmes (Clark et al., 1966, Normandin
et al., 2002, Ries et al., 1995, O'Donnell et al., 1998) high
intensity exercise appears to yield improved training results (Gimenez
et al., 2000, Coppoolse et al., 1999, Casaburi et al., 1991). It is
accepted that high intensity training at a heart rate at or above
anaerobic threshold or at a modified Borg dyspnoea score of above four
(Mejia et al., 1999) is recommended.

Casaburi et al (1991) suggest a training intensity of 80% maximal
oxygen consumption although the patient group in this study was younger
than those generally entering pulmonary rehabilitation programmes. The
British Thoracic Society (2001) recommends exercise should commence at a
level commensurate with 60% of maximal oxygen peak obtained from an
incremental shuttle walk test. Similarly, the American Thoracic Society
(1999) suggests 60--75% of maximum work load or if this cannot be
achieved, interval training of two --three minute training at high
intensity (60- 80% of maximum) with equal periods of rest. One of the
key messages from Emtner et al (2003) is that to achieve significant
clinical benefits from training, the exercise intensity needs to be as
high as possible. The training effects are only maintained if exercise
is continued and it is essential that patients are able to continue
exercising in the home environment.

It is recommended that oxygen requirements are established when the
patient is medically stable and prior to rehabilitation.
Physiotherapists are arguably ideally placed to perform the appropriate
assessment and prescription.

Field walk tests for assessment

An exercise test is considered mandatory before commencing
pulmonary rehabilitation to establish baseline exercise tolerance and
physiological parameters. This test is chosen according to its ability
to reflect the aims of the exercise programme and may also be used to
assess the need for training or ambulatory oxygen. Field walk tests are
highly suitable as they assess requirements during this functional
activity. The options for testing include:

a. The incremental shuttle walk test (ISWT)

The ISWT (Singh et al., 1992) was developed as a standardised walk
test, which is externally paced and incremented by increasing the walk
speed at minute intervals. It allows a measure of peak maximal oxygen
consumption to be estimated and has been validated in COPD patients.
Garrod et al (2000) used the ISWT as an outcome measure for
rehabilitation with training oxygen and demonstrated only minimal gains.
In the editorial accompanying this paper Calverley (2000) emphasised
that the greatest effects of oxygen are with endurance exercise and
hence the six minute walk test or the endurance shuttle walk test (ESWT)
may be more sensitive measures.

b. Six minute walk test (6 MWT)

The 6 MWT is a self paced test which is performed according to a
defined protocol (American Thoracic Society, 2002, Steele, 1996)). It is
highly reproducible when delivered in a standardised format, has been
shown to be sensitive, and is responsive to change with a validated
minimal clinically important difference of greater than 53 metres
(Radelmeier et al., 1997) The Auckland research group (Eaton et al.,
2002) used the 6 MWT to test the clinical utility of ambulatory oxygen
and demonstrated both an acute and short term response. Turner et al
(2004) reported that greater oxygen desaturation was observed during
field walk tests and suggested that both the 6 MWT and the ISWT are more
sensitive than cycle ergometry in detecting exercise induced hypoxaemia
and in assessing ambulatory oxygen therapy needs.

c. The endurance shuttle walk test (ESWT)

The ESWT was developed by Revill et al (1999) and uses the ISWT to
establish the walking pace. It is performed with externally controlled
pacing at a pace commensurate with 85% of the ISWT estimated maximal
oxygen consumption. It provides the same relative exercise intensity for
all patients and was shown to be more sensitive to change following
pulmonary rehabilitation than the ISWT. The Auckland research group
(Eaton et al., 2004) also found that the ESWT was more sensitive to
change following pulmonary rehabilitation when compared with the 6 MWT.
The ESWT has been used in a trial of ambulatory oxygen and an ambulatory
ventilator and demonstrated sensitivity to the acute application of
oxygen (Revill et al., 2000).

TRAINING OXYGEN

The provision of training oxygen during exercise can be used to
achieve higher training intensity. Patients who are hypoxemic at rest
and who are using LTOT are advised to exercise on oxygen, the flow rate
titrated to prevent saturations falling below 90% if possible. However
some patients with normal oxygen tension at rest profoundly desaturate
on exercise or during activities of daily living. In addition to
ventilation perfusion mismatch, in some patients with COPD, resting
hyperinflation, as reflected by increased residual functional capacity
and total lung capacity is present. Tidal breathing occurs at a less
advantageous portion of the diaphragmatic length--tension curve and
accessory muscle use is increased at rest. During exercise it is
difficult to increase tidal volume and hence an increased respiratory
rate is used to augment ventilation. This results in a decreased
expiratory time and consequent air trapping and further hyperinflation.
There is an increased work of breathing and respiratory muscle fatigue
occurs. Dynamic hyperinflation has been identified as a possible
mechanism which limits exercise in patients with COPD (O'Donnell
and Webb, 1993). Oxygen has been shown to decrease respiratory
frequency, minute ventilation and dynamic hyperinflation and improve
exercise performance (Somfay et al., 2001).

The evidence for training oxygen

Although laboratory studies (Somfay et al., 2001, Davidson et al.,
1988, Woodcock et al., 1981) showed application of training oxygen
increased exercise endurance, randomised controlled rehabilitation
studies (Garrod et al., 2000, Rooyackers et al., 1997) using training
oxygen for patients with exercise desaturation did not demonstrate
improved outcomes. However both of the latter studies had few patients
and may have failed to detect change. Also exercise training was at
lower intensity. More recently, Emtner et al (2003) unequivocally
demonstrated that the application of training oxygen delivered at three
litres/min during a seven week training programme resulted in improved
physical performance and health status. Non-hypoxemic, physically
inactive patients with severe COPD were able to train with a more rapid
progression of exercise intensity and increase of endurance in a steady
state exercise.

The British Thoracic Society (2001) suggest training oxygen should
be provided during exercise where clinically important desaturation,
defined as being less than 90%, has been found at the training load in
the preliminary test. It should be continued for similar activity at
home. Applying this guideline would need an increase in resource for
both ambulatory and training oxygen in New Zealand. Other guidelines
(American Thoracic Society 1999, ACCP/AACVPR 1997) do not address the
issue.

Emtner et al (2003) attempted to predict patients who would benefit
from oxygen during exercise. There was a significant correlation between
improvement in endurance time induced by oxygen versus room air in the
pre training tests, however it was not sufficiently high to predict
benefit accurately in individual subjects.

In carefully controlled study conditions it appears that training
oxygen may be of benefit but it remains to be established how this would
translate into routine clinical practice and guidelines remain
unsatisfactory. The suggestion is that the testing process establishes
individual need and benefit.

Assessment for training oxygen

The assessment protocol is the same regardless of the field walk
test selected.

1. A baseline field walk test is performed on room air according to
a standard protocol to ensure reproducibility and to establish the need
for assessment for oxygen.

It is important to allow sufficient recovery time between tests.
Recommended recovery times vary for the 6 MWT. American Thoracic Society
guidelines (1999) recommend one hour, while others (Steele, 1996,
Sciurba and Slivka, 1998) recommend 15-30 minutes. For the ESWT tests it
is recommended that 40 minutes be allowed (Revill et al., 1999)

American Thoracic Society (1995) advise that if the field walk test
shows a fall in saturation below 88% at maximum load then oxygen should
be provided. However it would seem that the degree of dyspnoea and
fatigue should also be considered (Griffiths et al., 2000). In most
rehabilitation programmes, continuous flow oxygen would be the delivery
of choice. The flow rate used during the test should be high enough to
maintain saturations above 90%.

2. Two further tests are performed on cylinder air and cylinder
oxygen. As there is a significant placebo effect to applying oxygen, the
tests are randomised and blinded with oximeters and cylinder labels
obscured from the patient.

* The patient rests for 10 minutes

* The gas is applied via nasal prongs at 4 litres per minute flow
rate and the patient rests for a further five minutes

* Baseline dyspnoea and oxygen saturation is measured. The most
usual measure of dyspnoea is the Modified Borg (1982) score of perceived
breathlessness. Continuous oximetry is employed during the test and
recorded at minute intervals

* The recovery time to baseline saturation and dyspnoea is also
recorded, as the rate at which breathlessness resolves may be a relevant
outcome (Calverley, 2000).

* The test is repeated with the second gas after an appropriate
interval.

Prescription of training oxygen

Oxygen should be prescribed for exercise if oxygen saturations can
be maintained close to 90% and there is a significant increase in walk
distance or a significant decrease in the dyspnoea score on cylinder
oxygen versus cylinder air. Royal College of Physicians (1999)
arbitrarily suggest a positive change of 10% over the baseline walking
distance and/or breathlessness score on room air after walking with
cylinder oxygen. Eaton et al (2002) used a distance greater than 53
metres or a decrease in the Borg dyspnoea score of one point to identify
an acute response to ambulatory oxygen. The flow rate should be titrated
according to the test results and further tests may be required. Snider
(2002) suggests that a flow rate of 6 litres/minute may be necessary in
some patients.

AMBULATORY OXYGEN

Provision of training oxygen is based on an acute response and the
oxygen is used while exercising during pulmonary rehabilitation or
exercising at home. Ambulatory oxygen is indicated for patients who are
established on LTOT who are mobile and need to leave the home on a
regular basis. It can also be prescribed for patients who do not fulfil
the criteria for LTOT but who desaturate severely on exertion, show
improvement in exercise capacity on oxygen, are mobile and are motivated
to use ambulatory oxygen outside the home.

In New Zealand, ambulatory oxygen is supplied by small portable
cylinders equipped with a demand delivery device that delivers the flow
rate only on inspiratory demand thus extending cylinder usage. There are
several different devices available all shown to improve arterial
oxygenation with lower flow rates than continuous oxygen. However some
devices appear to be more effective than others (Fuhrman et al., 2004).
The portable cylinders weigh approximately 2.7 kilograms and are
generally carried in a backpack. There is a measurable negative impact
from carrying the weight of the cylinder and an alternative may be to
use a trolley. Liquid oxygen has the advantage of being lighter to carry
but is not available in New Zealand.

The evidence for ambulatory oxygen

McDonald et al (1995) assessed the effects of ambulatory oxygen
used during activity at home on quality of life and concluded that
although there were small improvements in exercise performance, this did
not translate into improved quality of life. As studies show poor
compliance with the use ambulatory oxygen (Lock et al., 1991, Vergeret,
et al., 1989) careful patient selection is necessary. The Auckland
research group (Eaton et al., 2002) examined the clinical utility of
ambulatory oxygen and its effect on quality of life on those patients
with COPD and exertional desaturation who did not fulfil the criteria
for provision of LTOT. It was demonstrated that ambulatory oxygen is
associated with modest but clinically significant improvements in
quality of life particularly in the mastery domain and an increased
walking distance with decreased dyspnoea. The research also showed that
the benefits of ambulatory oxygen could not be predicted by the acute
response to cylinder oxygen and despite either an acute response or a
short term (6 weeks) response, a considerable number of patients (41%)
declined to continue with ambulatory oxygen due to poor tolerability. As
a result of this work, a rigorous screening and assessment protocol has
been developed.

Assessment for ambulatory oxygen

An essential prerequisite is that the patient should have completed
a pulmonary rehabilitation programme ensuring dyspnoea coping strategies
and fitness are maximised. It also acts as a convenient surrogate
measure of adherence and willingness to improve exercise tolerance.
Patients must be sufficiently ambulant, defined as being able to walk
further than 200 metres in six minutes, and have dyspnoea of sufficient
severity that it impacts on the ability to perform activities of daily
living outside the home. Patients must understand that ambulatory oxygen
is to be used to facilitate activity outside the home on a regular
basis. It needs to be emphasised that it is not for short burst use i.e.
pre-oxygenation before activity, breathlessness during recovery from
activity or control of breathlessness at rest. Oxygen used in this
manner has been shown to be generally ineffective (Lewis et al., 2003,
Stevenson and Calverley, 2004).

Assessment Protocol

Assessment takes place over three visits.

1. On the initial visit, the patient completes two field walk tests
on room air to ensure reproducibility and to ensure they fulfil the
criteria for further assessment. They are shown the equipment and
educated on the use of ambulatory oxygen so that they can make a more
informed decision to proceed with further assessment. If so, they are
asked to complete an activity diary for two weeks, which documents the
activities they have completed during that time, the time taken to do
them and the Modified Borg dyspnoea score on completion of each
activity. The patient's needs should be established and transparent
so that an alternative supply of oxygen for use inside the home to
facilitate activity may be considered.

2. After two weeks, the patient completes

* a further field walk test on room air

* a randomised, blinded trial of cylinder air versus cylinder
oxygen using the portable equipment

* a baseline Chronic Respiratory Questionnaire (Guyatt, et al.,
1993) using activities in the dyspnoea domain for which the patient will
use ambulatory oxygen

* a Hospital Anxiety and Depression score (Zigmond and Snaith,
1983)

The diaries are scrutinised and individual uses of ambulatory
oxygen identified.

As the acute response is not a predictor of longer term benefit,
this is followed by a six week clinical trial of cylinder oxygen.
Patients are instructed to continue with the activity diary.

3. After six weeks all of the baseline tests as performed at visit
two are repeated.

The main outcome measures of the clinical trial are a significant
improvement in quality of life as measured by the Chronic Respiratory
Questionnaire, improved exercise tolerance or dyspnoea and an
appropriate pattern of usage as demonstrated by the patient diary. As
most cylinders last a maximum of three hours, adequate usage has been
defined as being at least two cylinders per week.

Prescription of ambulatory oxygen

Careful scrutiny of all outcome measures and a willingness by the
patient to use the equipment outside the home is essential before
ambulatory oxygen is prescribed for long term use. In some cases the
patient's expectations of benefits are not met by the clinical
reality resulting in poor adherence and inappropriate use.

The prescription of flow rate is difficult as it is a balance
between maintaining oxygenation and the constraints of cylinder hours
available. The Auckland research group (Eaton et al., 2002) found that
even at four litres per minute, the maximum available with demand device
used in the trial, correction of hypoxaemia was only achieved in 54% of
patients and this factor did not predict short term response. The Royal
College of Physicians (1999) state that correction of hypoxaemia should
be achieved before provision of ambulatory oxygen. However this may not
be entirely realistic as correction of hypoxaemia may not be the only
mechanism, which improves exercise tolerance.

Patient follow up is imperative to determine the ongoing
appropriateness of ambulatory oxygen in the event of symptomatic
deterioration. It is also essential to check that the equipment and
prescribed flow rate continue to be appropriate for the patient. The
Auckland research group suggest an initial three-month follow up and
then six monthly thereafter.

CONCLUSION

Provision of training oxygen may enhance pulmonary rehabilitation
outcomes and maximise patient fitness levels by assisting the patient to
achieve a higher level of intensity during exercise training. Ambulatory
oxygen may assist patients to remain active within the community and so
improve their quality of life and exercise tolerance. The provision of
both modalities has considerable implication for resourcing and
therefore the assessment process should reflect the outcomes anticipated
in supplying these forms of oxygen therapy. The benefits will only be
realised if each decision is correct and appropriate to each individual
patient. Further studies are recommended to refine the guidelines and
assessment process. The Auckland research group has attempted to
standardise assessment processes in order to optimise clinical benefit
and ensure the best possible use of an often-scarce resource.

Acknowledgement

The author wishes to thank Dr. Tam Eaton for assistance, advice and
support during the preparation of the manuscript and in furthering the
practice of physiotherapy in the management of patients with COPD.